Returns a specification to start this module under a supervisor.

See Supervisor.

Extracts the tags defined on the event.

iex> event = %{
...>   "event_type" => "ClutchLaid", 
...>   "event_data" => %{"turtle_id" => "t1", "clutch_id" => "c1", "eggs" => 42}, 
...>   "event_tags" => ["turtle:t1", "clutch:c1"], 
...>   "stream_id" => "turtle_mating-1234",
...>   "stream_position" => 3
...> }
iex> Fact.EventTagsIndexer.index_event(event, [])
["turtle:t1", "clutch:c1"]

iex> event = %{
...>   "event_type" => "EggHatched", 
...>   "event_data" => %{"turtle_id" => "t2", "clutch_id" => "c1"}, 
...>   "event_tags" => ["turtle:t2", "clutch:c1"], 
...>   "stream_position" => 1
...> }
iex> Fact.EventTagsIndexer.index_event(event, [])
["turtle:t2", "clutch:c1"]

iex> event = %{
...>   "event_type" => "DatabaseCreated", 
...>   "event_data" => %{"database_id" => "RVX27QR6PFDORJZF24C4DIICSQ"}, 
...>   "stream_id" => "__fact", 
...>   "stream_position" => "1"
...> }
iex> Fact.EventTagsIndexer.index_event(event, [])
nil

Starts the indexer process.